Industrial installations are known, which comprise an active part in which the industrial process is carried out and a control and supervision position separate from the zone including the active part of the installation are known in the art. The active part of the industrial installation includes means for measurement, control and command which are associated with its various components in order to permit control and supervision thereof. These means for measurement, control and command are extremely numerous, and must be connected with the control position by an assembly of conductors permitting transmission of the information and the orders providing for the command and the control of the installation in operation.
In a complex industrial installation, the means for measurement, control and command are capable of providing for the acquisition, transmission and/or reception of information and of orders of very widely differing types. These items of information relate to parameters of the industrial process, such as temperature, pressure or throughout level, and likewise to positions of components such as gates or valves. In addition to the items of information relating to the industrial process, the system may transmit items of information originating from test materials or providing for communications between the operators or any other type of information.
In the case of certain industrial installations, the conditions prevailing within the zone including the active part of the installation make the acquisition, the transmission and/or the reception of the information or orders within this active zone extremely difficult.
This is so in the case of nuclear power stations including a pressurized water nuclear reactor, in which it is necessary to effect measurements within the building of the reactor, which is not accessible during the operation of this reactor. The requirement for a very high degree of reliability and for a high degree of accuracy on the part of the apparatus for acquisition and for transmission of data necessitates the operation, quite frequently, of inspections of the means for acquisition and for transmission of these data. It is likewise necessary to protect the same against the influence of the environment in which the industrial process is carried out.
In prior art systems, the data are acquired, transmitted and utilized in the form of electrical signals passing through conductors joining the control position to the active zone of the industrial installation. In the case where intense magnetic fields are developed within this active zone, it is necessary to isolate the conductors from these magnetic fields and, for example, to use screened cables for the passage of the conductors. This is so, for example, in metallurgical or steel making installations.
In all these cases, it is necessary to isolate the conductors in an efficient manner and to effect earthing of the components for protection of the cables and of their mechanical support. In certain installations, it is necessary to use coaxial cables involving high costs for the low level electrical signals and the digital data at high throughout. It is also necessary to provide devices for galvanic decoupling between the places where the information is taken.
In certain installations, it may be extremely dangerous to convey electric currents, even of low intensity, in the vicinity of substances or media which are inflammable or explosive. This is so, for example, in the case of petroleum or petro-chemical installations or installations for the processing of natural gas. These risks are still further increased in circumstances in which sources of current are necessary in the vicinity of the means for measurement, for command or for control within the active part of the installation.
On the other hand, in the case of complex installations including a large number of means for measurement and for control, and therefore a large number of links with the control position, it is necessary to reduce to the greatest possible extent the volume and the cost of the linking conductors used; it is likewise necessary to make provision for possibilities for increasing the number of links, in the event of a modification of the industrial process or of an improvement in this process necessitating a larger number of measurements or of inspections. In order to achieve these results, it has been proposed to use electronic multiplexers/demultiplexers, which permit at the same time a reduction of the number of links which are necessary between the active part of the installation and the control position and an increase of the number of points of measurement, of control or of command without increasing the number of links. However, such electronic multiplexers/demultiplexers are very costly and require local sources of supply, within the active part of the installation.
On the other hand, devices are known for telecommunication by optical means which permit the joining, by optical fibers, of the emitting positions to the receiving positions, with multiplexing and demultiplexing of the modulated optical signals circulating within the optical fibers. However, the use of such devices has not become general in circumstances in which it is desired to join a control position of an industrial installation to the active zone of such installation. The difficulty is, in fact, that such a device for teletransmission by optical fibers requires the establishment of luminous sources in the vicinity of the points of emission of the information and thus in the vicinity of the measurement sensors, within the active zone of the industrial installation which is being controlled and supervised. These luminous sources require, for the establishment thereof, the presence of electrical sources in the vicinity of the active components of the industrial installation.
It has been proposed, in U.S. Pat. No. 4,367,040, to supply temperature measurement sensors placed in different positions in a rotor by means of fixed optical sources independent of the rotor. A broad spectral band radiation is formed by coupling of these sources and directed into an optical device borne by the rotor ; that device carries out the division of the board spectral band radiation in order to obtain unitary radiations of different wavelengths which are each sent to a temperature sensor. No material link is present between the fixed optical sources and the rotor, and the luminous radiation having a broad spectral band is emitted in the direction of the rotor axis to be received by the optical device borne by the rotor. The length of the propagation path of the luminous radiation for reaching the rotor can be maintained at a very low value.
In the case of an industrial installation, the active zone of which must be separated by a great distance, from the zone where the luminous radiations are generated, such a method cannot be used.